Nitrogen-containing sintered hard alloy

ABSTRACT

A nitrogen-containing sintered hard alloy in which the content of the binder phase is at the highest level in an area to a depth of between 3 μm and 500 μm from its surface and its content in this area is between 1.1 and 4 times the average content of the binder phase in the entire alloy. Below this area, the content of the binder phase decreases gradually so that its content becomes equal to the average content of the binder phase at a depth of 800 μm or less. The content of the binder phase in the surface layer is 90% or less of its maximum value. The depth of 800 μm is a value at which the thermal conductivity is kept sufficiently high and at the same time a tool can keep high resistance to plastic deformation during cutting.

TECHNICAL FIELD

This invention relates to a nitrogen-containing sintered hard alloy which possesses excellent thermal shock resistance, wear resistance and toughness and which shows exceptionally favorable properties when used as a material for cutting tools.

Background Art

There are already known cutting tools that are formed of a nitrogen-containing sintered hard alloy having hard phases of carbonitrides or the like composed mainly of Ti and bonded together through a metal phase made up of Ni and Co. Such a nitrogen-containing sintered hard alloy is extremely small in particle size of the hard phases compared to a conventional sintered hard alloy that contains no nitrogen, so that it shows much improved high-temperature creep resistance. Because of this favorable property, this material has been used for cutting tools as widely as what is known as cemented carbides, which are composed mainly of WC.

But nitrogen-containing sintered hard alloys are low in thermal shock resistance. This is because (1) its main component, Ti carbonitride, is extremely low in thermal conductivity compared to WC, the main component of a cemented carbide, so that the thermal conductivity as the entire alloy is about half that of a cemented carbide, and (2) its thermal expansion coefficient, which also largely depends upon that of main component, is 1.3 times that of a cemented carbide. Therefore, cutting tools made of such an alloy have not been used with reliability under conditions where the tools are subjected to severe thermal shocks such as for milling, lathing of square materials or for wet copy cutting where the depth of cut changes widely.

The present inventors have analyzed various phenomena associated with cutting operations such as the temperature and stress distributions in cutting tools in different cutting types and Studied the relation between such phenomena and the arrangement of components in the tool. As a result, they achieved the following findings. A cemented carbide, which has a high thermal conductivity, is less likely to heat up because the heat produced at the tool surface during cutting diffuses quickly through the tool body. Also, due to its low thermal expansion coefficient, tensile stresses are less likely to be produced and remain at the surface area even if the tool begins idling abruptly or the high-temperature portion is brought into contact with a water-soluble cutting oil and thus is cooled sharply.

In contrast, nitrogen-containing sintered hard alloys composed mainly of Ti show a sharp temperature gradient during cutting due to its low thermal conductivity. Namely, heat is difficult to diffuse from the areas where the temperature is the highest during cutting, such as the tip of the cutting edge and a portion of the rake face where chips collide, so that the temperature is high at the surface but is much lower at the inside. Once such an alloy gets a crack, it can be broken very easily because of low inner temperature. Conversely, if such an alloy is cooled sharply by contact with a cutting oil, the temperature gradient is reversed, that is, only the surface area is cooled sharply while the temperature at the inner portion directly thereunder remains high. Due to this fact and high thermal expansion coefficient, tensile stresses tend to be produced at the surface area, which dramatically increases the possibility of thermal cracks. Namely, it was difficult to sufficiently improve the thermal conductivity and thermal expansion coefficient of nitrogen-containing sintered hard alloys which contain Ti, a component necessary for a good surface finish. The inventors have carried out extensive studies for solutions to these problems and reached the present invention.

DISCLOSURE OF THE INVENTION

The nitrogen-containing sintered hard alloy according to the present invention has a Ti-rich layer at a superficial layer which determines the characteristics of the cut surface finish, and with a predetermined thickness provided right under the superficial layer a layer rich in binding metals such as Ni and Co. Since the Ni/Co-rich layer has a high thermal expansion coefficient, this layer serves to impart compressive stresses to the surface layer when cooled after sintering or detaching the cutting tool. Besides, tungsten, an essential component of the hard phase, should be rich inwardly from the surface. By gradually increasing the W content inwardly, the hard phase serves to increase the thermal conductivity of the alloy, especially in the inner area thereof, though it is the binder phase that mainly serves this purpose. Namely, since the binder phase is present in a smaller amount and the hard phase in a larger amount in the deeper area of the binder phase-rich layer, it is possible to improve the thermal conductivity effectively.

More particularly, the nitrogen-containing sintered hard alloy of the present invention is characterized in that the content of the binder phase is at the highest level in an area to a depth of between 3 μm and 500 μm from its surface and its content in this area should be between 1.1 and 4 times the average content of the binder phase in the entire alloy. Below this area, the content of the binder phase should decrease gradually so that its content becomes equal to the average content of the binder phase at a depth of 800 μm or less. The content of the binder phase in the surface layer is 90% or less of its maximum value. The depth of 800 μm is a value at which the thermal conductivity is kept sufficiently high and at the same time the tool can keep high resistance to plastic deformation. during cutting. As for the hard phase, we have discovered that Ti, as well as Ta, Nb and Zr, which can improve the wear resistance of the alloy when cutting steel materials to a similar degree as Ti, should be present in greater amounts in the surface area, and instead, W and Mo should be present in smaller amounts in the surface area. In particular, W should not be present in the surface area as WC particles or should be present in the amount of 0.1 volume % or less. The hard phase is made up of at least one of caribides, nitrides, carbonitrides and compositions thereof of at least two transition metals that belong in Groups IVb, Vb and VIb of the Periodic Table.

We will now discuss reasons why the above conditions are necessary:

(1) Range of depth of the layer in which the content of binder phase is at the highest level and the maximum content

The binder phase-rich region is necessary to increase the tool strength and to produce compressive stresses in the surface layer when the cutting tool cools after sintering and when it is detached. If the depth of the binder phase-rich layer is less than 3 μm, the tool's wear resistance will be insufficient. If more than 500 μm, it would be difficult to produce a sufficiently large compressive stress in the surface layer. If the ratio of the highest content of the binder phase to the average binder phase content is 1.1 or less, no desired tool strength would be attainable. If the ratio exceeds 4, the tool might suffer plastic deformation when cutting or it might get too hard at its inner area to keep sufficiently high tool strength.

(2) Content of binder phase in the surface layer

The surface layer has to be sufficiently wear-resistant and also has to have a smaller thermal expansion coefficient than the inner area so that compressive stresses are applied to the surface layer. Should the ratio to the highest binder phase content exceed 0.9, these effects would not appear.

(3) Contents of Ti, Ta, Nb and Zr in the surface layer

The surface layer has to have high wear resistance and thus has to contain in large amounts not only Ti but Ta, Nb and Zr, which can improve the wear resistance of the material as effectively as Ti. If the ratio of X at the surface to the average X value of the entire alloy is less than 1.01, no desired wear resistance is attainable. Ta and Nb are especially preferable because these elements can also improve the high-temperature oxidation resistance. By providing the surface layer rich in these elements, it is possible to improve various properties of the finished surface.

(4) W and Mo contents in the hard phase in the surface layer

The contents of W and Mo in the hard phase are represented by y and b in the formulas (Ti_(x) W_(y) M_(c)) and (Ti_(x) W_(y) Mo_(b) M_(c)).

The surface layer should contain WC and/or Mo₂ C in smaller amounts because these elements are low in wear resistance. Eventually, the amounts of W and/or Mo in the inner hard phase are greater. It is practically impossible to prepare a material that contains W so that the ratio of Y in the surface to y in the entire alloy will be less than 0.1. If this ratio exceeds 0.9, the wear resistance will be too low to be acceptable. Mo behaves in the hard phase in substantially the same way as WC.

Now focusing on WC only, W in the hard phase, which increases in amount inwardly of the alloy from its surface, may be present in the form of WC particles or may be present at the peripheral region of complex carbonitride solid solutions. In the hard phase, the W-rich solid solutions may partially appear or may be greater in amount than the surface. It is also possible to improve the thermal conductivity and strength by increasing the ratio of hard particles having a white core and a dark-colored peripheral portion when observed under a scanning electron microscope (such particles are called white-cored particles; the white portions are rich in W, while the dark-colored portions are poor in W). The values x and y have to be within the ranges of 0.5<X≦0.95, 0.05<Y≦0.5 in order to maintain high wear resistance and heat resistance. Out of these ranges, both the wear resistance and heat resistance will drop to a level at which the object of the present invention is not attainable.

As a result of extensive studies in search of means to improve the thermal shock resistance, wear resistance and toughness, the present inventors have discovered that it is most effective to impart compressive residual stresses to the surface area of a nitrogen-containing sintered hard alloy. As discussed above, tensile stress acts on the surface area of a nitrogen-containing sintered hard alloy with changing thermal environment. If this stress exceeds the yield strength of the sintered hard alloy itself, cracks (thermal cracks) will develop, thus lowering the strength of the nitrogen-containing sintered hard alloy. Such an alloy is destined to be broken sooner or later. From the above discussion, it means that the best way to improve the thermal shock resistance is to improve its yield strength.

The most effective way to improve the yield strength of a nitrogen-containing sintered hard alloy is to impart compressive residual stresses to its surface region. Before discussing the detailed structure and mechanism for imparting compressive residual stresses, we would like to point out the fact that by imparting compressive residual stresses, it is possible not only to improve the thermal shock resistance of a nitrogen-containing sintered hard alloy but to significantly improve its wear resistance and toughness when compared to conventional alloys of this type.

The nitrogen-containing sintered hard alloy according to the present invention is heated under vacuum. Sintering (at 1400° C.-1550° C.) is carried out in a carburizing or nitriding atmosphere to form a surface layer comprising a Ti-rich hard phase with zero or a small amount of binder phase. The alloy is then cooled in a decarburizing atmosphere so that the volume percentage of the binder phase will increase gradually inwards from the surface of the alloy. By controlling the cooling rate to 0.05-0.8 times the conventional cooling rate, it is possible to increase the content of binder phase rapidly inwards from the surface and thus to impart desired compressive residual stresses to the surface area.

In this arrangement, since the surface area is composed only of a Ti-based hard phase (or such a hard phase plus a small amount of a metallic phase), the alloy shows excellent wear resistance compared to conventional nitrogen-containing sintered hard alloys. Its toughness is also superior because the layer right under the surface area is rich in binder phase.

Also, we have discovered that by sintering a material powder containing 10 wt % or more WC in a nitriding atmosphere, it is possible to form a nitrogen-containing sintered hard alloy in which WC particles appear with the WC volume percentage increasing toward the average WC volume percentage from the alloy surface inwards. Since the surface area is for the most part composed of the Ti-based hard phase, the alloy is sufficiently wear-resistant. Also, the WC particles present right under the alloy surface allow smooth heat dispersion and thus reduce thermal stress. Such WC particles also serve to increase the Young's modulus and thus the toughness of the entire nitrogen-containing sintered hard alloy. In the nitrogen-containing sintered hard alloy according to the present invention, metallic components or metallic components and WC may ooze out of the alloy surface in small quantities. But the surface layer formed by such components will have practically no influence on the cutting performance because the thickness of such a layer does not exceed 5 μm.

As discussed above, by applying compressive residual stresses to the surface area, it is possible to increase the yield strength of the entire alloy. The present inventors have also discovered that by controlling such compressive residual stresses at 40 kg/mm² or more in the hard phase at the surface layer, the thermal shock resistance increases to a level higher than that of a conventional nitrogen-containing sintered hard alloy and comparable to that of a cemented carbide.

Also, compressive residual stresses greater than the stresses at the outermost surface area should preferably be applied to the intermediate area from the depth of 1 μm to 100 μm from the surface. With this arrangement, even if deficiencies should develop in the outermost area, the compressive stresses applied to the intermediate area will suppress the propagation of cracks due to deficiencies, thereby preventing the breakage of the alloy itself. In order to distribute stresses in the above-described manner, the binder phase has to be distributed as shown in FIG. 5. Namely, by distributing the binder phase as shown in FIG. 5, stresses are distributed as shown in FIG. 6.

By setting the maximum compressive residual stress at a value 1.01 times or more greater than the compressive residual stresses in the uppermost area, it is possible to prevent the propagarion of cracks very effectively, provided the above-mentioned conditions are all met. By setting this maximum value at 40 kg/mm² or more, the alloy shows resistance to crack propagation comparable to that of a cemented carbide. But, as will be inferred from FIGS. 5 and 6, if the maximum compressive residual stress were present at a depth of more than 100 μm compressive residual stresses in the uppermost area would decrease. This is not desirable because the thermal shock resistance unduly decreases. Also, a hard and brittle surface layer that extends a width of more than 100 μm would reduce the toughness of the alloy.

Thus, an area containing 5% by volume or less of the binder phase should be present between the depth of 1 μm and 100 μm. With this arrangement, the alloy would show excellent wear resistance while not resulting any decrease in toughness.

Preferably, the area in which the content of the binder phase is zero or not more than 1% by volume should have a width of between 1 μm and 50 μm (see FIG. 7).

The present inventors have studied the correlation between compressive residual stresses and the distribution of the binder phase from the alloy surface inwards and discovered that the larger the content gradient of the metallic binder phase (the rate at which the content increases inwardly per unit distance), the larger the compressive residual stress near the point at which the content of the binder phase begins to increase (see FIG. 7).

Further studies also revealed that, in order for the alloy to have a thermal shock resistance comparable to that of a cemented carbide, the inward content gradient of the binder phase (the rate at which the content of the binder phase increases per micrometer) should be 0.05% by volume or higher. Also, in order for the alloy to have higher wear resistance and toughness than conventional nitrogen-containing sintered hard alloys, the content of the binder phase in the area between the surface of the alloy and the point at which it begins to increase should be 5% by volume or less, and also such an area has to have a width between 1 μm and 100 μm.

By distributing WC particles in the alloy so that its content is higher in the inner area of the alloy than in the surface area, it is possible to improve the toughness in the inner area of the alloy while keeping high wear resistance intrinsic to Ti in the surface area. For higher wear resistance, the WC content in the area from the surface to the depth of 50 μm should be limited to 5% by volume or less. The alloy containing WC particles shows improved thermal conductivity. Its thermal shock resistance is also high compared to a nitrogen-containing sintered hard alloy containing no WC particles. Moreover, such an alloy is less likely to get broken because of improved Young's modulus.

Thus, by forming cutting tools from the alloys according to the present invention, it is possible to increase the reliability of such tools even if they are used under cutting conditions where they are subjected to severe thermal shocks such as in milling, lathing of square materials or for wet copy cutting where the depth of cut changes widely.

Since the nitrogen-containing sintered hard alloy according to the present invention has high thermal shock resistance comparable to that of a cemented carbide, it will find its use not only for cutting tools but as wear-resistant members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the distribution of components in Specimen 1 in Example 1 according to the present invention, with distance from its surface in the direction of depth;

FIG. 2 is a similar graph of Specimen 2 in Example 1;

FIG. 3 is a similar graph of Specimen 3 in Example 1;

FIG. 4 is a similar graph of Specimen 4 in Example 1;

FIG. 5 is a graph showing one example of distribution of the binder phase in an alloy according to the present invention;

FIG. 6 is a graph showing the distribution of compressive residual stress in the binder phase shown in FIG. 5; and

FIG. 7 is a graph showing the relation between the distribution of Co as the binder phase and the strength.

BEST MODE FOR EMBODYING THE INVENTION Example 1

A powder material made up of 48% by weight of (Ti₀.8 W₀.2)(C₀.7 N₀.3) powder having an average particle diameter of 2 μm, 24% by weight of (TaNb)C powder (TaC: NbC=2:1 (weight ratio)) having an average particle diameter of 1.5 μm, 19% by weight of WC powder having an average particle diameter of 4 μm, 3% by weight of Ni powder and 6% by weight of Co powder, both having an average particle diameter of 1.5 μm, were wet-mixed, molded by stamping, degassed under a vacuum of 10⁻² Torr at 1200° C., heated to 1400° C. at a nitrogen gas partial pressure of 5 Torr and a hydrogen gas partial pressure of 0.5 Torr, and sintered for one hour first under a vacuum of 10⁻² Torr and then in a gaseous atmosphere. The material sintered was cooled quickly with nitrogen to 1330° C. and then cooled gradually at the rate of 2° C./min while supplying CO₂ at 100 Torr. Specimen 1 was thus obtained. Its structure is shown in Table 1.

For comparison purposes, we also prepared three additional Specimens 2-4 using conventional process. Namely, Specimen 2 was formed by sintering the same stamped molding as in Specimen 1 at 1400° C. under a nitrogen partial pressure of 5 Torr. Specimen 3 was formed by sintering the same stamped molding in the same manner as with Specimen 2 and further cooling it at a CO partial pressure of 200 Torr. Specimen 4 was formed by sintering the same stamped molding in the same manner as with Specimen 2 and further cooling it at a nitrogen partial pressure of 180 Torr. Table 2 show their structures.

Specimens 1-4 were actually used for cutting under three different cutting conditions shown in Table 3 and tested for the three items shown in Table 3. The test results are shown in Table 4.

Example 2

A powder material made up of 51% by weight of (Ti₀.8 W₀.2)(C₀.7 N₀.3) powder having an average particle diameter of 2 μm, 27% by weight of (TaNb)C powder (TaC: NbC=2:1 (weight ratio)) having an average particle diameter of 1.2 μm, 11% by weight of WC powder having an average particle diameter of 5 μm, 3% by weight of Ni powder and 8% by weight of Co powder, both having an average particle diameter of 1.5 μm, were wet-mixed, molded by stamping, degassed under a vacuum of 10⁻² Torr at 1200° C., and sintered for one hour at 1450° C. under a nitrogen gas partial pressure of 10 Torr. Specimen 5 was obtained by cooling the thus sintered material under a high vacuum of 10⁻⁵ Torr. Specimen 6 was formed by cooling the same sintered molding in CO₂.

For comparison purposes, we also prepared from the same stamped moldings Specimens 7 and 8 having the structures shown in Table 5. These specimens were subjected to actual cutting tests under the cutting conditions shown in Table 6. The test results are shown in Table 7.

Example 3

A powder material made up of 42% by weight of (Ti₀.8 W₀.2)(C₀.7 N₀.3) powder having an average particle diameter of 2.5 μm, 23% by weight of (TaNb)C powder (TaC: NbC =2:1 (weight ratio)) having an average particle diameter of 1.5 μm, 25% by weight of WC powder having an average particle diameter of 4 μm, 2.5% by weight of Ni powder and 6.5% by weight of Co powder, both having an average particle diameter of 1.5 μm, were wet-mixed, molded by stamping, and sintered for one hour at 1430° C. under a nitrogen gas partial pressure of 15 Torr. Specimen 9 was obtained by cooling the thus sintered material in CO₂. Specimen 10 was formed by cooling the same sintered material in hydrogen gas having a dew point of -40° C.

For comparison purposes, we also prepared from the same powder material Specimens 11-13 so that the average content of binder phase and content of hard phase (Ti +Nb, W) will be as shown in Table 8. We also prepared other Specimens 14-19, which have different structures from Specimens 9 and 10 though they were formed from the same stamped molding as Specimens 9 and 10. These specimens were subjected to actual cutting tests under the cutting conditions shown in Table 9. The test results are also shown in Table 9.

Example 4

We prepared a powder material made up of 85% by weight of (Ti₀.75 Ta₀.04 Nb₀.04 W₀.17)(C₀.56 N₀.44) having a black core and a white periphery as observed under a reflecting electron microscope and having an average particle diameter of 2 μm, 8% by weight of Ni powder and 7% by weight of Co powder, both having an average particle diameter of 1.5μm. The powder materials thus prepared were wet-mixed, molded by stamping, degassed at 1200° C. under vacuum of 10⁻² Torr, and sintered for one hour at 1450° C. under a nitrogen gas partial pressure of 10 Torr, and cooled in CO₂. Specimen 20 was thus obtained. Specimen 21 was formed by mixing Ti(CN), TaC, WC, NbC, Co and Ni so that the mixture will have the same composition as Specimen 20 and sintering the mixture.

For comparison purposes, we also prepared Specimens 22 and 23 having structures shown in Table 10 from the same molding as used in forming Specimen 20, and Specimen 24 having a structure shown in Table 10 from the same molding as used in forming Specimen 21. These specimens were subjected to actual cutting tests under the cutting conditions shown in Table 11. The test results are also shown in Table 11.

Example 5

We prepared alloy specimens having average compositions and structures as shown in Table 12 from (Ti₀.8 W₀.2)(C₀.7 N₀.3) powder having an average particle diameter of 2. μm, TaC powder having an average particle diameter of 1.5 μm, WC powder having an average particle diameter of 4 μm, ZrC powder having an average particle diameter of 2 μm, and Ni powder and Co powder, both having an average particle diameter of 1.5 μm. Table 13 shows the properties of the respective alloy specimens.

Example 6

We prepared alloy specimens having average compositions and structures as shown in Table 14 from (Ti₀.8 W₀.2 ) (C₀.7 N₀.3 ) powder having an average particle diameter of 2 μm, TaC powder having an average particle diameter of 5 μm, NbC powder having an average particle diameter of 3 μm, WC powder having an average particle diameter of 4 μm, Mo₂ C powder having an average particle diameter of 3 μm, and Ni powder and Co powder, both having an average particle diameter of 1.5 μm. Table 15 shows the properties of the respective alloy specimens.

Example 7

We prepared the following material powders (a)-(f): (a) 82% by weight of (Ti₀.7, W₀.2, Nb₀.05, Ta₀.05)(C₀.7, N₀.3) powder having an average particle diameter of 1.5 μm, 12% by weight of Ni powder having an average particle diameter of 1.5 μm, and 6% by weight of Co powder having an average particle diameter of 1.5 μm

(b) 49% by weight of (Ti₀.9, W₀.05, Nb₀.025, Ta₀.025)(C₀.7, N₀.3) powder having an average particle diameter of 1.5 μm, 37% by weight of WC powder having an average particle diameter of 2 μm, and Ni powder and Co powder, 7% by weight each, both having an average particle diameter of 1.5 μm (c) 82% by weight of (Ti₀.6, W₀.2, Nb₀.2)(C₀.7, N₀.3) powder having an average particle diameter of 1.5 μm, and Ni powder and Co powder, 9% by weight each, both having an average particle diameter of 1.5m

(d) 49% by weight of (Ti₀.8, W₀.1, Nb₀.1)(C₀.4, N₀.6) powder having an average particle diameter of 1.5μm, 37% by weight of WC powder having an average particle diameter of 2 μm, and Ni powder and Co powder, 7% by weight each, both having an average particle diameter of 1.5 μm (e) 82% by weight of (Ti₀.7, W₀.3)(C₀.7, N₀.3) powder, having an average particle diameter of 1.5 μm, 12% by weight of Ni powder having an average particle diameter of 1.5 μm, and 6% by weight of Co powder also having an average particle diameter of 1.5 μm (f) 49% by weight of (Ti₀.7, W₀.3) (C₀.7, N₀.3) powder having an average particle diameter of 1.5μm, 37% by weight of WC powder having an average particle diameter of 2 μm, and Ni powder and Co powder, 7% by weight each, both having an average particle diameter of 1.5 μm.

These material powders were wet-mixed and molded by stamping to a predetermined shape. Then, they were heated under vacuum, sintered at 1400° C.-1550° C. in a carburizing or nitriding atmosphere, and cooled under vacuum. Specimens A-1-A-5, B-1-B-8, and C-1-C-6 were thus formed.

Table 16 shows the compressive residual stresses for Specimens A-1-A-5. Compressive residual stresses were measured by the X-ray compressive residual stress measuring method. We calculated stresses using the Young's modulus of 46000 and the Poisson's ratio of 0.23.

Specimens A-1-A-5 were subjected to cutting tests under the cutting conditions shown in Table 17 and evaluated for three items shown in Table 17. Test results are shown in Table 18.

Example 8

Table 19 shows the distribution of the binder phase in each of Specimens B-1-B-8.

Specimens B-1-B-8 were subjected to cutting tests under the conditions shown in Table 20 and evaluated for three items shown in Table 20. Test results are shown in Table 21.

Example 9

Table 22 shows the compressive residual stresses and the distribution of the binder phase for each of Specimens C-1-C-6.

Specimens C-1-C-6 were subjected to cutting tests under the conditions shown in Table 23 and evaluated for three items shown in Table 23. Test results are shown in Table 24.

                                      TABLE 1                                      __________________________________________________________________________     Binder phase rich layer                                                                           Binder                                                                              Hard phase                                             Average                                                                             Max. Depth                                                                               Thick-                                                                             phase                                                                               in    Hard phase in                                    binder                                                                              binder                                                                              at which                                                                            ness                                                                               at   inner layer                                                                          surface layer                                    phase                                                                               phase                                                                               content                                                                             of rich                                                                            surface                                                                             Ti W  Ti  W                                            content                                                                             content                                                                             is max.                                                                             layer                                                                              layer                                                                               con-                                                                              con-                                                                              con-                                                                               con-                                         (wt %)                                                                              (wt %)                                                                              (μm)                                                                             (μm)                                                                            (wt %)                                                                              tent                                                                              tent                                                                              tent                                                                               tent                                                                               Remarks                                  __________________________________________________________________________     9    15   56   180 5    55 25 85  7   WC particles                                  Ratio to      Ratio to   Ratio                                                                              Ratio                                                                              deposit inside                                average       max.       to  to                                                content       content    inner                                                                              inner                                             1.67          0.3        1.5 0.3                                          __________________________________________________________________________      (Atomic % in hard phase)                                                 

                                      TABLE 2                                      __________________________________________________________________________     Binder phase                                                                                      Thick-      Hard phase                                      Aver-   Portion where content                                                                     ness             Surface                                    age     is max.    of  Surface        Ratio                                    con-    Con-                                                                              Ratio   rich                                                                               Con-    Inner  to                                       Speci-                                                                             tent                                                                               tent                                                                              to  Depth                                                                              layer                                                                              tent                                                                               Ratio                                                                              Ti                                                                               W  Ti                                                                               inner                                                                              W  Ratio                             men (wt %) aver-                                                                              (μm) (wt %)                                                                             to  (Atomic % in hard phase)                                                                     to                                No. ↓                                                                           ↓                                                                          age ↓                                                                           ↓                                                                           ↓                                                                           max.                                                                               ↓                                                                         ↓                                                                          ↓                                                                             ↓                                                                          inner                             __________________________________________________________________________     2   9   9  1.0*                                                                               20* ˜ Inner*                                                                     5   0.6*                                                                               55                                                                               25 50                                                                               0.9*                                                                               29 1.0*                                      (Increase gradually from                                                       surface to inner)                                                      3   9   9  1.0*                                                                               --* --* 9   1.0*                                                                               55                                                                               25 55                                                                               1.0*                                                                               25 1.0*                                         Uni-                       Uni-                                                form                       form                                     4   9   13 1.4 0*  30  13  1.0*                                                                               55                                                                               25 72                                                                               1.3 12 0.5                               __________________________________________________________________________      (*Out of the range of the present invention)                             

                                      TABLE 3                                      __________________________________________________________________________             Cutting condition 1                                                                       Cutting condition 2                                                                       Cutting condition 3                              __________________________________________________________________________     Tool Shape                                                                             CNMG432    CNMG432    CNMG432                                          Work piece                                                                             SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                        Round bar  Round bar with 4                                                                          Round bar                                                           longitudinal grooves                                        Cutting speed                                                                          200 m/min  100 m/min  250 m/min                                        Feed    0.28 mm/rev.                                                                              0.38 mm/rev.                                                                              0.20 mm/rev                                      Depth of cut                                                                           1.5 mm     2.0 mm     1.5→2.0 mm                                Cutting oil                                                                            Water soluble                                                                             Not used   Water soluble                                    Cutting time                                                                           15 min     30 sec     15 min                                           Judgement item                                                                         Wear on flank (mm)                                                                        Number of chipped                                                                         Number of chipped                                                   edges among 20                                                                            edges among 20                                                      cutting edges                                                                             cutting edges                                    __________________________________________________________________________

                  TABLE 4                                                          ______________________________________                                                             Cutting                                                                        condition 2                                                          Cutting   Number of  Cutting condition 3                                       condition 1                                                                              chipped edges                                                                             Number of chipped                                         Wear on   among 20   edges among 20                                  Specimen No.                                                                             flank (mm)                                                                               cutting edges                                                                             cutting edges                                   ______________________________________                                         Present 1     0.11       4        2                                            invention                                                                      Compara-                                                                               2     0.15      17       20                                            tive    3     0.24      10       12                                            example 4     0.35       8        6                                            ______________________________________                                    

                                      TABLE 5                                      __________________________________________________________________________               Binder phase                                                                                  Thick-      Hard phase                                          Aver-                                                                              Portion where content                                                                     ness        Inner                                                                               Surface                                        age is max.    of  Surface Ti   Ti                                                                               Ratio                                        con-                                                                               Con-                                                                              Ratio   rich                                                                               Con-    +    + to                                 Speci-    tent                                                                               tent                                                                              to  Depth                                                                              layer                                                                              tent                                                                               Ratio                                                                              Ta W Ta                                                                               inner                                                                              W  Ratio                       men       (wt %) aver-                                                                              (μm) (wt %)                                                                             to  (Atomic % in hard phase)                                                                     to                          No.       ↓                                                                           ↓                                                                          age ↓                                                                           ↓                                                                           ↓                                                                           max.                                                                               ↓                                                                          ↓                                                                         ↓                                                                             ↓                                                                          inner                       __________________________________________________________________________     Present                                                                              5   11  14 1.3 140 360 6   0.43                                                                               68 21                                                                               77                                                                               1.13                                                                               13 0.62                        inven-                                                                               6   11  27 2.4 15  100 4   0.15                                                                               68 21                                                                               84                                                                               1.24                                                                                9 0.43                        tion                                                                           Compara-                                                                             7   11  11.5                                                                              1.05*                                                                              20  360 9   0.78                                                                               68 21                                                                               70                                                                               1.03                                                                               18 0.86                        tive  8   11  15 1.36                                                                               85  250 9   0.6 68 21                                                                               68                                                                               1.0*                                                                               21 1.0*                        example                                     Uni-                                                                           form                               __________________________________________________________________________      (*Out of the range of the present invention)                             

                                      TABLE 10                                     __________________________________________________________________________                                          Hard phase                                          Binder phase               Inner                                                                               Surface                                                       Thick-      Ti   Ti                                             Aver-                                                                              Portion where content                                                                     ness        +    +                                              age is max.    of  Surface Ta   Ta Ratio                                       con-                                                                               Con-                                                                              Ratio   rich                                                                               Con-    +    +  to                                Speci-    tent                                                                               tent                                                                              to  Depth                                                                              layer                                                                              tent                                                                               Ratio                                                                              Nb W Nb inner                                                                              W Ratio                       men       (wt %) aver-                                                                              (μm) (wt %)                                                                             to  (Atomic % in hard phase)                                                                     to                          No.       ↓                                                                           ↓                                                                          age ↓                                                                           ↓                                                                           ↓                                                                           max.                                                                               ↓                                                                          ↓                                                                         ↓                                                                              ↓                                                                         inner                       __________________________________________________________________________     Present                                                                              20  15  28 1.87                                                                               8   140 5   0.18                                                                               83 17                                                                               92 1.11                                                                               8 0.47                        inven-                                                                         tion                                                                           Compara-                                                                             21  15  25 1.67                                                                               5   100 4   0.16                                                                               83 17                                                                               98.5                                                                              1.19                                                                               1.5                                                                              0.08*                       tive  22  15  21 1.4  0*  20 21  1.0*                                                                               83 17                                                                               94 1.13                                                                               6 0.35                        example                                                                              23  15  16 1.07*                                                                              8   170 7   0.39                                                                               83 17                                                                               92 1.11                                                                               8 0.47                              24  15  25 1.67                                                                                2*  10 9   0.36                                                                               83 17                                                                               97 1.17                                                                               3 0.18                        __________________________________________________________________________      (*Out of the range of the present invention)                             

                  TABLE 6                                                          ______________________________________                                                  Cutting condition 4                                                                         Cutting condition 5                                      ______________________________________                                         Tool shape CNMG432        CNMG432                                              Work piece SCM435 (HB = 250)                                                                             SCM435 (HB = 250)                                               Round bar      Round bar                                            Cutting speed                                                                             180 m/min      200 m/min                                            Feed       0.25 mm/rev.   0.20 mm/rev.                                         Depth of cut                                                                              1.5 mm         1.7→0.2 mm                                    Cutting oil                                                                               Water soluble  Water soluble                                        Cutting time                                                                              20 min         15 min                                               Judgement item                                                                            Wear on flank (mm)                                                                            Number of chipped                                                              edges among 20                                                                 cutting edges                                        ______________________________________                                    

                  TABLE 7                                                          ______________________________________                                                                  Cutting condition 5                                                            Number of chipped                                                Cutting condition 4                                                                          edges among 20                                        Specimen No.                                                                              Wear on flank (mm)                                                                           cutting edges                                         ______________________________________                                         Present  5     0.13          2                                                 invention                                                                               6     0.11          3                                                 Compara- 7     0.16          18                                                tive     8     0.35          4                                                 example                                                                        ______________________________________                                    

                                      TABLE 8                                      __________________________________________________________________________               Binder phase                                                                                  Thick-      Hard phase                                          Aver-                                                                              Portion where content                                                                     ness        Inner                                                                               Surface                                        age is max.    of  Surface Ti   Ti                                                                               Ratio                                        con-                                                                               Con-                                                                              Ratio   rich                                                                               Con-    +    + to                                 Speci-    tent                                                                               tent                                                                              to  Depth                                                                              layer                                                                              tent                                                                               Ratio                                                                              Nb W Nb                                                                               inner                                                                              W  Ratio                       men       (wt %) aver-                                                                              (μm) (wt %)                                                                             to  (Atomic % in hard phase)                                                                     to                          No.       ↓                                                                           ↓                                                                          age ↓                                                                           ↓                                                                           ↓                                                                           max.                                                                               ↓                                                                          ↓                                                                         ↓                                                                             ↓                                                                          inner                       __________________________________________________________________________     Present                                                                               9   9  18 2.0 100 240 6   0.33                                                                               62 29                                                                               82                                                                               1.32                                                                               13 0.45                        inven-                                                                               10   9  27 3.0 85  450 4   0.15                                                                               62 29                                                                               79                                                                               1.27                                                                               15 0.52                        tion                                                                           Compara-                                                                             11  11  12 1.09*                                                                              20  130 3   0.25                                                                               65 21                                                                               77                                                                               1.18                                                                                8 0.38                        tive  12   5  21 4.2*                                                                                0*  10 21  1.0*                                                                               71 18                                                                               78                                                                               1.10                                                                                3 0.17                        example                                                                              13  15  18 1.2  8  118 4   0.22                                                                               68 21                                                                               92                                                                               1.35                                                                                2 0.09*                             14  9   9.5                                                                               1.06*                                                                              15  120 7   0.74                                                                               62 29                                                                               69                                                                               1.11                                                                               10 0.34                              15  9   38 4.22*                                                                              5    35 22  0.58                                                                               62 29                                                                               75                                                                               1.21                                                                                8 0.28                              16  9   12 1.33                                                                               10   30 11  0.92*                                                                              62 29                                                                               81                                                                               1.31                                                                               12 0.41                              17  9   18 2.0 120 110 7   0.74                                                                               62 29                                                                               82                                                                               1.0*                                                                               27 0.93*                             18  9   18 2.0 40  230 4   0.44                                                                               62 29                                                                               82                                                                               1.42                                                                                2 0.07*                             19  9   15 1.67                                                                                2*  10 6   0.67                                                                               62 29                                                                               82                                                                               1.32                                                                               13 0.45*                       __________________________________________________________________________      (*Out of the range of the present invention)                             

                  TABLE 9                                                          ______________________________________                                                       Cutting                                                                        condition 6                                                                             Cutting Condition 7                                     ______________________________________                                         Cutting  Tool shape CNMG432    CNMG432                                         conditions                                                                              Work piece SCM435     SCM435                                                              (HB = 250) (HB = 250)                                                          Round bar  Round bar                                                Cutting speed                                                                             220 m/min  180 m/min                                                Feed       0.25 mm/rev.                                                                              0.21 mm/rev.                                             Depth of cut                                                                              1.5 mm     2.5→0.3 mm                                        Cutting oil                                                                               Water soluble                                                                             Water soluble                                            Cutting time                                                                              10 min     10 min                                                   Judgement  Wear on    Number of chipped                                        item       flank (mm) edges among 20                                                                 cutting edges                                   Specimen No.                                                                            Present   9    0.15      4                                                     invention                                                                               10    0.18      1                                                     Com-     11    0.16     10                                                     para-    12    0.48     18                                                     tive     13    Chipped off                                                                              8                                                     example        in 5 min                                                                 14    0.25     15                                                              15    0.63     12                                                              16    0.23     12                                                              17    0.32     14                                                              18    Chipped off                                                                              6                                                                    in 7 min                                                                 19    Over 0.8 mm                                                                              8                                                                    in 5 min                                               ______________________________________                                    

                  TABLE 11                                                         ______________________________________                                                       Cutting                                                                        condition 8                                                                             Cutting Condition 9                                     ______________________________________                                         Cutting  Tool shape CNMG432    CNMG432                                         conditions                                                                              Work piece SCM435     SCM435                                                              (HB = 250) (HB = 250)                                                          Round bar  Round bar                                                Cutting speed                                                                             200 m/min  200 m/min                                                Feed       0.32 mm/rev.                                                                              0.21 mm/rev.                                             Depth of cut                                                                              1.5 mm     1.5→0.1 mm                                        Cutting oil                                                                               Water soluble                                                                             Water soluble                                            Cutting time                                                                              15 min     15 min                                                   Judgement  Wear on    Number of chipped                                        item       flank (mm) edges among 20                                                                 cutting edges                                   Specimen No.                                                                            Present  20    0.10     3                                                      invention                                                                      Com-     21    Chipped off                                                                             6                                                      para-          in 13 min                                                       tive     22    Over 0.8 mm                                                                             8                                                      example        in 10 min                                                                23    0.23     14                                                              24    Chipped off                                                                             15                                                                    in 10 min                                              ______________________________________                                    

                  TABLE 13                                                         ______________________________________                                                       Cutting  Cutting                                                               condition 10                                                                            Condition 11                                            ______________________________________                                         Cutting  Tool shape CNMG432    CNMG432                                         conditions                                                                              Work piece SCM435     SCM435                                                              (HB = 250) (HB = 250)                                                          Round bar  Round bar                                                Cutting speed                                                                             200 m/min  250 m/min                                                Feed       0.25 mm/rev.                                                                              0.22 mm/rev.                                             Depth of cut                                                                              1.5 mm     2.5→0.2 mm                                        Cutting oil                                                                               Water soluble                                                                             Water soluble                                            Cutting time                                                                              20 min     10 min                                                   Judgement  Wear on    Number of chipped                                        item       flank (mm) edges among 20                                                                 cutting edges                                   Specimen No.                                                                            Present  25    0.15      2                                                     invention                                                                               26    0.11      3                                                     Com-     27    0.24     10                                                     para-    28    Chipped off                                                                             18                                                     tive           in 15 min                                                       example                                                               ______________________________________                                    

                                      TABLE 12                                     __________________________________________________________________________               Binder phase                                                                                  Thick-      Hard phase                                          Aver-                                                                              Portion where content                                                                     ness        Inner                                                                               Surface                                        age is max.    of  Surface Ti   Ti                                                                               Ratio                                        con-                                                                               Con-                                                                              Ratio   rich                                                                               Con-    +    + to                                 Speci-    tent                                                                               tent                                                                              to  Depth                                                                              layer                                                                              tent                                                                               Ratio                                                                              Zr W Zr                                                                               inner                                                                              W  Ratio                       men       (wt %) aver-                                                                              (μm) (wt %)                                                                             to  (Atomic % in hard phase)                                                                     to                          No.       ↓                                                                           ↓                                                                          age ↓                                                                           ↓                                                                           ↓                                                                           max.                                                                               ↓                                                                          ↓                                                                         ↓                                                                             ↓                                                                          inner                       __________________________________________________________________________     Present                                                                              25  12  28 2.33                                                                               60  140 6   0.21                                                                               72 19                                                                               82 1.14                                                                                6                                                                               0.32                        invention                                                                            26   9  27 3.0 95  245 5   0.19                                                                               68 24                                                                               79 1.16                                                                               15                                                                               0.63                        Compara-                                                                             27  12  12 1.0*                                                                                0* 160 12  1.0*                                                                               70 21                                                                               77 1.10                                                                                8                                                                               0.38                        tive  28   9  21 2.33                                                                               10  120 7   0.33                                                                               58 35                                                                               83 1.43                                                                                3                                                                               0.08*                       example                                                                        __________________________________________________________________________      (*Out of the range of the present invention)                             

                                      TABLE 14                                     __________________________________________________________________________               Binder phase                                                                                  Thick-      Hard phase                                          Aver-                                                                              Portion where content                                                                     ness        Inner                                                                               Surface                                        age is max.    of  Surface   W    Ratio                                                                              W                                        con-                                                                               Con-                                                                              Ratio   rich                                                                               Con-      +    to  +                              Speci-    tent                                                                               tent                                                                              to  Depth                                                                              layer                                                                              tent                                                                               Ratio                                                                              Ti                                                                               Mo Ti                                                                               inner                                                                              Mo Ratio                       men       (wt %) aver-                                                                              (μm) (wt %)                                                                             to  (Atomic % in hard phase)                                                                     to                          No.       ↓                                                                           ↓                                                                          age ↓                                                                           ↓                                                                           ↓                                                                           max.                                                                               ↓                                                                         ↓                                                                          ↓                                                                             ↓                                                                          inner                       __________________________________________________________________________     Present                                                                              29  14  28 2.0 15  40  7   0.25                                                                               61                                                                               29 82                                                                               1.34                                                                               6  0.21                        inven-                                                                         tive                                                                           Compara-                                                                             30  13  14 1.08*                                                                              20  60  11  0.79                                                                               70                                                                               24 75                                                                               1.07                                                                               8  0.33                        tive                                                                           example                                                                        __________________________________________________________________________      (*Out of the range of the present invention)                             

                  TABLE 15                                                         ______________________________________                                                       Cutting  Cutting                                                               condition 12                                                                            Condition 13                                            ______________________________________                                         Cutting  Tool shape CNMG432    CNMG432                                         conditions                                                                              Work piece SCM435     SCM435                                                              (HB = 250) (HB = 250)                                                          Round bar  Round bar                                                Cutting speed                                                                             120 m/min  150 m/min                                                Feed       0.29 mm/rev.                                                                              0.28 mm/rev.                                             Depth of cut                                                                              1.5 mm     1.5→0.2 mm                                        Cutting oil                                                                               Water soluble                                                                             Water soluble                                            Cutting time                                                                              20 min     20 min                                                   Judgement  Wear on    Number of chipped                                        item       flank (mm) edges among 20                                                                 cutting edges                                   Specimen No.                                                                            Present  29    0.13      3                                                     invention                                                                      Com-     30    0.24     12                                                     para-                                                                          tive                                                                           example                                                               ______________________________________                                    

                                      TABLE 16                                     __________________________________________________________________________     Compressive residual stress                                                    Speci-   Compressive residual                                                                      Max. compressive                                                                        / Distance from                                   men      stress at surface                                                                         residual stress                                                                         / surface                                         No. Material                                                                            (kg/mm.sup.2)                                                                             (kg/mm.sup.2)                                                                           / (μm)                                         __________________________________________________________________________     A-1*                                                                               (a)  11         11       / 0                                               A-2*                                                                               (c)  32         32       / 0                                               A-3 (a)  54         54       / 0                                               A-4 (e)  54         66       / 25                                              A-5*                                                                               (a)   0          0       / 0                                               __________________________________________________________________________      *Out of the range of the present invention                               

                                      TABLE 17                                     __________________________________________________________________________             Cutting condition 1                                                                       Cutting condition 2                                                                       Cutting condition 3                                      (lathing)  (lathing)  (milling)                                        __________________________________________________________________________     Tool Shape                                                                             CNMG432    CNMG432    CNMG432                                          Work piece                                                                             SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                        Round bar  Round bar with 4                                                                          Round bar                                                           longitudinal grooves                                        Cutting speed                                                                          180 (m/min)                                                                               110 (m/min)                                                                               160 (m/min)                                      Feed    0.30 (mm/rev.)                                                                            0.30 (mm/rev.)                                                                            0.28 (mm/rev)                                    Depth of cut                                                                           1.5 (mm)   2.0 (mm)   2.0 (mm)                                         Cutting oil                                                                            Water soluble                                                                             Not used   Water soluble                                    Cutting time                                                                           15 (min)   30 (sec)   5 passes                                         Judgement item                                                                         Wear on flank (mm)                                                                        Number of chipped                                                                         Total number of                                                     edges among 20                                                                            thermal cracks among                                                cutting edges                                                                             20 cutting edges                                 __________________________________________________________________________

                  TABLE 18                                                         ______________________________________                                         Speci- Cutting   Cutting condition 2                                                                          Cutting condition 3                             men    condition 1                                                                              Number of chipped                                                                            Number of thermal                               No.    Wear (mm) edges         cracks                                          ______________________________________                                         A-1*   0.28      11            72                                              A-2*   0.24      8             65                                              A-3    0.14      3              4                                              A-4    0.13      0              2                                              A-5*   0.36      18            140                                             ______________________________________                                          *Out of the range of the present invention                               

                                      TABLE 19                                     __________________________________________________________________________     Structure                                                                               Binder phase                                                                          Width of area where binder                                     Speci-   content at                                                                            phase content is constant                                                                    Increment of binder phase                        men      surface                                                                               at not more than 5 vol %                                                                     content per unit distance                        No. Material                                                                            (vol %)                                                                               (μm)       (vol %/μm)                                    __________________________________________________________________________     B-1*                                                                               (a)  7      None          0.02                                             B-2 (c)  3      None          0.02                                             B-3 (e)  3       4            0.03                                             B-4 (c)  3       8            0.07                                             B-5 (a)  0      None          0.03                                             B-6 (a)  0      10            0.04                                             B-7 (a)  0      15            0.09                                             B-8*                                                                               (a)  14     None          0                                                __________________________________________________________________________      *Out of the range of the present invention                               

                                      TABLE 20                                     __________________________________________________________________________             Cutting condition 1                                                                       Cutting condition 2                                                                       Cutting condition 3                                      (lathing)  (lathing)  (milling)                                        __________________________________________________________________________     Tool Shape                                                                             CNMG432    CNMG432    CNMG432                                          Work piece                                                                             SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                        Round bar  Round bar with 4                                                                          Plate with 3                                                        longitudinal grooves                                                                      grooves                                          Cutting speed                                                                          200 (m/min)                                                                               100 (m/min)                                                                               180 (m/min)                                      Feed    0.36 (mm/rev.)                                                                            0.32 (mm/rev.)                                                                            0.24 (mm/edge)                                   Depth of cut                                                                           1.5 (mm)   1.8 (mm)   2.0 (mm)                                         Cutting oil                                                                            Water soluble                                                                             Not used   Water soluble                                    Cutting time                                                                           10 (min)   30 (sec)   5 passes                                         Judgement item                                                                         Wear on flank (mm)                                                                        Number of chipped                                                                         Total number of                                                     edges among 20                                                                            thermal cracks among                                                cutting edges                                                                             20 cutting edges                                 __________________________________________________________________________

                  TABLE 21                                                         ______________________________________                                         Speci- Cutting   Cutting condition 2                                                                          Cutting condition 3                             men    condition 1                                                                              Number of chipped                                                                            Number of thermal                               No.    Wear (mm) edges         cracks                                          ______________________________________                                         B-1    0.25      15            101                                             B-2    0.17      10            80                                              B-3    0.12      8             53                                              B-4    0.10      4             13                                              B-5    0.10      8             29                                              B-6    0.08      6             22                                              B-7    0.06      3              4                                              B-8*   0.28      19            133                                             ______________________________________                                          *Out of the range of the present invention                               

                                      TABLE 22                                     __________________________________________________________________________     Compressive residual stress                                                                                 Distance from surface of                          Speci-   Compressive residual                                                                      Max. compressive                                                                        point where compressive                           men      stress at surface                                                                         residual stress                                                                         residual stress is max.                           No. Material                                                                            (kg/mm.sup.2)                                                                             (kg/mm.sup.2)                                                                           (μm)                                           __________________________________________________________________________     C-1 (a)  80         90       10                                                C-2 (b)  75         85       10                                                C-3*                                                                               (c)   0          0       0                                                 C-4 (d)   0          0       0                                                 C-5 (e)  65         65       0                                                 C-6 (f)  60         60       0                                                 __________________________________________________________________________     Structure                                                                            Binder phase                                                                           Width of area where binder                                             content at                                                                             phase content is constant                                                                    Increment of binder phase                          Specimen                                                                             surface at not more than 5 vol %                                                                     content per unit distance                          No.   (vol %) (μm)       (vol %/μm)                                      __________________________________________________________________________     C-1   0       10            0.10                                               C-2   0       10            0.10                                               C-3*  12      None          0                                                  C-4   12      None          0                                                  C-5   3       None          0.06                                               C-6   3       None          0.06                                               __________________________________________________________________________     Behavior of WC particles from surface area to inner area                       __________________________________________________________________________     C-1                                                                               Not present                                                                 C-2                                                                               2 vol % at surface, gradually increase with depth, become constant at          depth of 100 μm                                                          C-3*                                                                              Not present                                                                 C-4                                                                               3 vol % at surface, gradually increase with depth, become constant at          depth of 100 μm                                                          C-5                                                                               Not present                                                                 C-6                                                                               3 vol % at surface, gradually increase with depth, become constant at          depth of 100 μm                                                          __________________________________________________________________________      *Out of the range of the present invention                               

                                      TABLE 23                                     __________________________________________________________________________             Cutting condition 1                                                                       Cutting condition 2                                                                       Cutting condition 3                                      (lathing)  (lathing)  (milling)                                        __________________________________________________________________________     Tool Shape                                                                             CNMG432    CNMG432    CNMG432                                          Work piece                                                                             SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                                                         SCM435 (HB = 250)                                        Round bar  Round bar with 4                                                                          Plate with 3                                                        longitudinal grooves                                                                      grooves                                          Cutting speed                                                                          210 (m/min)                                                                               120 (m/min)                                                                               180 (m/min)                                      Feed    0.36 (mm/rev.)                                                                            0.32 (mm/rev.)                                                                            0.24 (mm/edge)                                   Depth of cut                                                                           1.5 (mm)   1.8 (mm)   2.5 (mm)                                         Cutting oil                                                                            Water soluble                                                                             Not used   Water soluble                                    Cutting time                                                                           8 (min)    30 (sec)   5 passes                                         Judgement item                                                                         Wear on flank (mm)                                                                        Number of chipped                                                                         Total number of                                                     edges among 20                                                                            thermal cracks among                                                cutting edges                                                                             20 edges                                         __________________________________________________________________________

                  TABLE 24                                                         ______________________________________                                         Speci- Cutting   Cutting condition 2                                                                          Cutting condition 3                             men    condition 1                                                                              Number of chipped                                                                            Number of thermal                               No.    Wear (mm) edges         cracks                                          ______________________________________                                         C-1    0.16      3             11                                              C-2    0.19      0              6                                              C-3*   0.37      19            121                                             C-4    0.39      11            95                                              C-5    0.22      8             52                                              C-6    0.23      4             26                                              ______________________________________                                          *Out of the range of the present invention                                

We claim:
 1. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein an area where the content of said binder phase becomes maximum exists in the region of depth of 3 μm to 500 μm from the surface; the maximum value of the binder phase content in weight percent is 1.1 to 4 times the average content of said binder phase in the entire alloy; said binder phase content decreases to said average content before the depth reaches 800 μm; the content of binder phase at the surface does not exceed 0.9 time said maximum value; said hard phase has a composition represented by (Ti_(x) W_(y) M_(c)) (where M is a hard phase-forming transition metal other than Ti and W, and x, y and c are atomic ratios and satisfy the relation x+y+c=1 (0.5<x≦0.95, 0.05<y 0.5)); x at the surface is 1.01 times or more the average x in the entire alloy, and y at the surface is 0.1 to 0.9 time the average y in the entire alloy; the values x and y at the surface return to said average x and y, respectively, before the depth reaches 800 μm; and WC particles do not exist at all or exist in the amount of not more than 0.1% by volume at the surface.
 2. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein an area where the content of said binder phase becomes maximum exists in the region of depth of 3 μm to 500 μm from the surface; the maximum value of the binder phase content in weight percent is 1.1 to 4 times the average content of the binder phase in the entire alloy; said maximum binder phase content decreases to said average value before the depth reaches 800 μm; the content of binder phase at the surface does not exceed 0.9 time said maximum value; said hard phase has a composition represented by (Ti_(x) W_(y) M'_(b) M_(c)) (where M is a hard phase-forming transition metal other than Ti, W, Ta and Nb, M' is selected from Ta and Nb, and x, y, b and c are atomic ratios and satisfy the relation x+y+b+c=1 (0.5<x ≦0.95, 0.05<y≦0.5, 0.01<b 0.4)); x+b at the surface is 1.01 times or more the average (x+b) in the entire alloy, and y at the surface is 0.1 to 0.9 time the average y in the entire alloy; the values (x+b) and y at the surface return to said average (x+b) and y, respectively, before the depth reaches 800 μm; and WC particles do not exist at all or exist in the amount of not more than 0.1% by volume at the surface.
 3. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein an area where the content of said binder phase becomes maximum exists in the region of depth of 3 μm to 500 μm from the surface; the maximum value of the binder phase content in weight percent is 1.1 to 4 times the average content of said binder phase in the entire alloy; said maximum binder phase content decreases to said average value before the depth reaches 800 μm; the content of binder phase at the surface does not exceed 0.9 time said maximum value; the hard phase has a composition represented by (Ti_(x) W_(y) Ta_(a) Nb_(b) M_(c)) (where M is a hard phase-forming transition metal other than Ti, W, Ta and Nb, and x, y, a, b and c are atomic ratios and satisfy the relation x+y+a+b+c=1 (0.5<x≦0.95, 0.05<y≦0.5, 0.01<a≦0.4, 0.01<b ≦0.4)); (x+a+b) at the surface is 1.01 times or more the average (x+a+b) in the entire alloy, and y at the surface is between 0.1 to 0.9 time the average y in the entire alloy; the values (x+a+b) and y at the surface return to said average values (x+a+b) and y, respectively, before the depth reaches 800 m; and WC particles do not exist at all or exist in the amount of not more than 0.1% by volume at the surface.
 4. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein an area where the content of said binder phase becomes maximum exists in the region of depth of 3 μm to 500 μm from the surface; the maximum value of the binder phase content in weight percent is 1.1 to 4 times the average content of said binder phase in the entire alloy; said maximum binder phase content decreases to said average value before the depth reaches 800 μm; the content of binder phase at the surface does not exceed 0.9 time said maximum value; said hard phase has a composition represented by (Ti_(x) W_(y) Zr_(b) M_(c)) (where M is a hard phase-forming transition metal other than Ti, W and Zr, and x, y, b and c are atomic ratios and satisfy the relation x+y+b+c=1 (0.5<x≦0.95, 0.05<y≦0.5, 0.01<b≦0.4)); (x+b) at the surface is 1.01 times or more the average (x+b) in the entire alloy, and y at the surface is 0.1 to 0.9 time the average y in the entire alloy; the values (x+b) and y at the surface return to said average values (x+b) and y, respectively, before the depth reaches 800 μm; and WC particles do not exist at all or exist in the amount of not more than 0.1% by volume at the surface.
 5. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein an area where the content of said binder phase becomes maximum exists in the region of depth of 3 μm to 500 μm from the surface; the maximum value of the binder phase content in weight percent is 1.1 to 4 times the average content of said binder phase in the entire alloy; said maximum binder phase content decreases to said average value before the depth reaches 800 μm; the content of binder phase at the surface does not exceed 0.9 time said maximum value; said hard phase has a composition represented by (Ti_(x) W_(y) Mo_(b) M_(c)) (where M is a hard phase-forming transition metal other than Ti, W and Mo, and x, y, b and c are atomic ratios and satisfy the relation x+y+b+c=1 (0.5<x≦0.95, 0.05<y≦0.5, 0.01<b<0.4)); x at the surface is 1.01 times or more the average x in the entire alloy, and (y+b) at the surface is 0.1 to 0.9 time the average (y+b) in the entire alloy; the values x and (y+b) at the surface return to said average values x and (y+b), respectively, before the depth reaches 800 μm; and WC particles do not exist at all or exist in the amount of not more than 0.1% by volume at the surface.
 6. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein the compressive residual stress in a hard phase having the crystal structure of NaCl type is 40 kg/mm.sup. 2 or more at the surface.
 7. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein a hard phase having the crystal structure of NaCl type and having a compressive residual stress 1.01 times or more than the compressive residual stress at the surface exists in the region of depth of 1 μm to 100 μm from the surface.
 8. A nitrogen-containing sintered hard alloy as claimed in claim 7 wherein said hard phase having the crystal structure of NaCl type in said region has a compressive residual stress of 40 kg/mm² or more.
 9. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein the content of said binder phase is not more than 5% by volume in a region from the surface of the alloy to a depth of between 1 μm and 100 μm, and wherein the content of said binder phase is between 10% by volume and 20% by volume at a depth of 800 μm from the surface of the alloy.
 10. A nitrogen-containing sintered alloy as claimed in claim 9 wherein a region from the surface to the depth of between 1 μm and 50 μm contains the binder phase in the amount of between zero and one percent by volume.
 11. A nitrogen-containing sintered hard alloy as claimed in claim 9 or 10 further having a structure wherein said alloy has a region in which the content of said binder phase increases gradually inwards from the surface of the alloy, and the maximum content gradient of the binder phase in said region in the direction of depth (the rate at which the binder phase content increases per micrometer) is 0.05% by volume.
 12. A nitrogen-containing sintered hard alloy as claimed in claim 11 having a structure wherein said alloy contains WC particles, the content of said WC particles increasing gradually inwards from the surface of the alloy and becoming equal to the average WC content in volume percentage in the entire alloy at a depth of 500 μm or less.
 13. A nitrogen-containing sintered alloy as claimed in claim 9 or 10 wherein the content of said binder phase is constant in a region from the surface to the depth of between 1 μm and 30 μm.
 14. A nitrogen-containing sintered hard alloy as claimed in claim 13 further having a structure wherein said alloy has a region in which the content of said binder phase increases gradually inwards from the surface of the alloy, and the maximum content gradient of the binder phase in said region in the direction of depth (the rate at which the binder phase content increases per micrometer) is 0.05% by volume.
 15. A nitrogen-containing sintered hard alloy as claimed in claim 14 further having a structure wherein said alloy contains WC particles, the content of said WC particles increasing gradually inwards from the surface of the alloy and becoming equal to the average WC content in volume percentage in the entire alloy at a depth of 500 μm or less.
 16. A nitrogen-containing sintered hard alloy as claimed in claim 13 further having a structure wherein said alloy contains WC particles, the content of said WC particles increasing gradually inwards from the surface of the alloy and becoming equal to the average WC content in volume percentage in the entire alloy at a depth of 500 μm or less.
 17. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein said alloy has a region in which the content of said binder phase increases gradually inwards from the surface of the alloy, and the maximum content gradient of the binder phase in said region in the direction of depth (the rate at which the binder phase content increases per micrometer) is 0.05% by volume.
 18. A nitrogen-containing sintered hard alloy as claimed in any of claims 10 or 17 further having a structure wherein said alloy contains WC particles, the content of said WC particles increasing gradually inwards from the surface of the alloy and becoming equal to the average WC content in volume percentage in the entire alloy at a depth of 500 μm or less.
 19. A nitrogen-containing sintered hard alloy comprising:a hard phase selected from the group consisting of:i) a hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti; and ii) a hard phase which is a combination of a first hard phase made up of composite carbonitrides of Ti and at least one transition metal selected from Group IVb, Vb, and VIb metals of the Periodic Table except Ti, and a second hard phase made up of at least one of carbides, nitrides and carbonitrides of at least one transition metal selected from Group IVb, Vb and VIb metals of the Periodic Table; and a binder phase containing Ni, Co and inevitable impurities, wherein said alloy contains WC particles, the content of said WC particles increasing gradually inwards from the surface of the alloy and becoming equal to the average WC content in volume percentage in the entire alloy at a depth of 500 μm or less. 